8/13/2019 ic50144a005t2g(.pi.*) Electron distribution in some low-spin mixed-ligand complexes of iron(III)

1/6

Merrithew, Lo, and ModestinoChem. , nt . Ed . Engi ., 4 672 (1965); b) 1. Ugi, and R. Meyer, Org.Syn., 411. 101 (1961).(a) W . P. Weber and G . \V. Gakel, Tetrahedron Lerr., 17, 1637 (1972);(b) W . P. Weber, C . W . Gokci, and I. Ugi, Angew. Chem., In?.Ed. Engl.,11. 530 119721.(a) Dy F.'Evans, J . Chem. SOC., 003 (1959); (b) R. A. Bailey, J . Chern.E d u c . , 49, 291 (1972).B. K . Figgis and .T Lewis, "'Modern Co ordination Chemistry,' ' J. Lcwisand R . G. W ilkins, Ed.. Interscizncc, Kew York, N. Y., 1960. p 403.4 Booth and J . Cha t t , J . Chem. Soc.. 2099 (1962) .C. A . Tolman, J . Amer . Chem. Soc., 92, 2956 (1970).C. A . Tolman, J . A m w . C h ~ m . ot.. 92, 2953 (1970).17. Boilatti and C. Llinghetti, J . Orgunometa/. Chem. . 22, 195 (1970).L. Malatcsra, A . Sacco, and G . Padod, Ann . Chief . R o m e ) ,43, 617(1953).15. . . Horrocks, Jr., and R . H . Liann, Specfrochiin . Acru, 19. 1375(1963).

Contribution from the Department of Chemistry,Worces ter Polytechnic Institute, Worces ter, Massac husctts 01609

P. B. M ERRIT 'HEW,* c...c. O, and A,. J. w m m m oReceived Apri l 22, 1974 A IC 4 0 2 6 2 0The temperature dependence of Ihr: quadri ipole splitting o f [Fe(bipy)2(CN)2]C104, [Fe(phen)2(CN)2]C104, H[Fe -(bipy)(CN)4]*2HzO.and H [ -e(phenj(C:nl)4].EH20 w a s obtained in the range 80-300'. Electron paramagnetic resonancespectra were obtained at ' 7 7 O on pure samples o f these complexes. These data were interpreted to give the magnitude ofthe spin-orbit coupling constant and the splitting of the tzg +) orbitals. The results are found to be consistent with earlierstudies of &Fe(CN)6 and, X'e(bipy)3(CIO4)3.

Nui nemu s low-spin S = l / z j ison(iI1) complexes o f theform [Fe ] 1--3 and [FeB3] ?-9 where B is a biden tate ligand,have been stu died by Mossbauer spectroscopy in an effort tocharacterize the cubic t2g(+) or t ? g ( ~ ) f the ligands areconsidered as back-bonding) orbitals. Thc relative energiesof the cubic t ~ 7 p * )orbitals in high-spin S z 2 j mixed-ligandcomplexes of i ro n (1 I ) have also been extensively investigatedby Mossbau er spectroscopy.l@-I' Until recently little attentionhad been paid to mixed-ligand complexes of iron(Iii1). Reiffand DeSirnone,'3 in an electron paramagnetic, resonance (ep r)and magnetically perturbed Mossbauer spectral study of[Fe(bipy)2(CN)2]+ (b ipy = 2,2'-bipyridine) and [Fe-(phen)z(CN)2]+ (plien = 1,1O-p~cnanthroline),uggested thatthe complexes exhibit trigonal distostio ns. W e have inves-tigated t he epr spe ctra, Mossbauer spectroscopy quadrupolesplitting dat a, an d magne tic susceptibilities o f the compounds[Fe(bipy)z (CN 2j C10.1, [F e ( phe n ) z ( C Nj r ]CiQ4, H [Fe-(bipy)(CN)4].2H28, and H[Fe(phen)(GIV4)].2142a3 in anattem pt to character ize the perturbation of the cubic 2 T z gground term of these complexes.E~~~~~~~~~~~ection

Preparation of Compounds. The compounds [Fe(bipy)z(CN)z]-C l o d , [Fe(phe n)z(CN )z] ClO4, [F e ( b i p y ) ~ ( C N ) z ] 03 [Fe-(p h en )2 (CN)2 ]NQ~ 4 HzQ, 3 Fe(bipy)(CP;)aj 2 P I z 0 and H [Fe-(phen)(CN)4] .2H20 mere prepared according to the, methods o fSchilt . 14Physical Measurements. The Mossbauer spectrometer and as-sociated cryostat have been described previously.2 The reproducibilityof the spectrometer over the period of a typical ssmple run (24 hr)is better than 0.5%. The spectrometer was calibrated by employingNa2[Fe(CS)sNO].2H2O as a standard with the quadrupole splittingtaken as 1.726 mm/sec . The spectra were fitted with a least-squaresprogram and th e relative error was determined statistically. l5 I t isthis error which is given in Table I. The absolute error, due toinadequacies in the calibration procedure, is estimated to be less than1%.The epr spectra of [Fe(bipy)z(GN)2]C104 and H[Fe(bipy)-(GN)4].2E-I20 were obtained 011 instrumen tation describe d previou.sly.9A Varian E -9 spectrometer system at X-band frequency was employed

Table E. Q u a d r u p o l e Splitting D a t aQuadrupole Quadrupolesplitt ing, splitting,mm/sec T e r n p , O K mmlsecemp, I